A Family of New Cobalt-Base Permanent Magnet Materials

Abstract

The magnetocrystalline anisotropy of several intermetallic phases of the type RCo5 (R = Y, Ce, Pr, Sm, Y-rich and Ce-rich mischmetals) has been investigated, and it is concluded that these alloys are promising candidates for fine-particle permanent magnets. They have extremely high uniaxial anisotropy (K = 5.4 to 7.7 × 107 erg/cm3), single easy axis, high saturation (Bs = 8500 to 11 200 G) and Curie point (tc = 464° to 747°C). Approximate upper limits for the possible energy product lie between 18 and 31.3 MGOe. Experimentally, coercive forces of over 8000 Oe and (BH)max = 5.1 MGOe have been observed in SmCo5 merely ground at room temperature. Grinding of YCo5 and (Ce-MM) Co5 produces an increase of MHc to 2200 and 2700 Oe, respectively, followed by a decrease as particle size continues to decrease.